The objective of the proposed research continues to be a comprehensive, systematic, and parametric evaluation of the roles that spectral locus and temporal variation play in selected binaural experiments. One major theme of the proposed experiments concerns across-frequency interactions that influence binaural processing (Aims 1 and 2). A second theme of the proposed experiments concerns sensitivity to interaural disparities that occur only during temporally discrete portions of longer sounds (Aim 3). One subset of experiments is designed to assess how, and under what conditions, the binaural auditory system combines, across frequency, interaural timing information. These experiments stem from our recent success in describing complex lateralization phenomena in terms of a cross-correlation model in which binaural images are formed by emphasizing or weighting, temporally-coincident activity across frequency channels that monitor the same interaural delays. A second subset of experiments is designed to reveal interactions among monaural and binaural processes. They capitalize on our recent discovery that the binaural masking produced by aural distortion products can be exploited in order to gain a better understanding of the capabilities and limitations of interaural delay mechanisms. A third subset of experiments is designed to measure sensitivity to interaural disparities that occur during temporally discrete portions of longer sounds. We will measure sensitivity to interaural temporal disparities (ITDs) and interaural intensitive differences (IIDs) as a function of when the target interaural disparity occurs and where, in terms of frequency- region it occurs. Both low-frequency and high-frequency target spectral regions will be employed. In one set of conditions, the values of the parameters of the stimuli being tested (e.g., spectral locus, time of occurrence of the interaural disparity) will be held constant throughout a block of trials. In another set of conditions they will be varied on a trial-by-trial basis. These uncertainty conditions will extend our recent findings that, under certain conditions, varying the center frequency of the stimuli on a trial-by-trial basis can produce devasting deficts in the detectability of ITDs, especially at the higher frequency regions. The potential health benefits of this program of research are a better understanding of how the ear and brain process information and the potential for better diagnostic procedures that may, eventually, have clinical significance.